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Abstract:

A silicon optical waveguide for transmitting an optical signal input to
the optical waveguide with a first frequency. The optical waveguide
includes a plurality of modulator circuits configured along a silicon
optical transmission channel. Each modulator circuit includes at least
one resonant structure that resonates at the first frequency when the
modulator circuit that includes the at least one resonant structure is at
a resonant temperature. Each modulator circuit has a different resonant
temperature.

Claims:

1. An optical waveguide, comprising: an optical transmission channel for
transmitting an optical signal input to the optical waveguide with a
first frequency; and a plurality of modulator circuits configured along
the optical transmission channel, each modulator circuit comprising at
least one resonant structure that resonates at the first frequency when
the modulator circuit that includes the at least one resonant structure
is at a resonant temperature, each modulator circuit having a different
resonant temperature.

2. The optical waveguide of claim 1, wherein the plurality of modulator
circuits are in series with each other.

3. The optical waveguide of claim 2, wherein the at least one resonant
structure is an optical modulator coupled to the optical transmission
channel.

4. The optical waveguide of claim 2, wherein the plurality of modulator
circuits each include an optical modulator coupled to the optical
transmission channel via an input switch and an output switch.

5. The optical waveguide of claim 4, wherein the at least one resonant
structure comprises the input switch.

6. The optical waveguide of claim 2, wherein the at least one resonant
structure has a maximum resonance at a respective resonant temperature.

7. The optical waveguide of claim 6, wherein the at least one resonant
structure is partially resonant at temperatures within a range of
temperatures bounding the structure's respective resonant temperature.

8. The optical waveguide of claim 7, wherein the range of temperatures
for the at least one resonant structure corresponding to each modulator
circuit overlaps the range of temperatures for at least one resonant
structure corresponding with a different modulator circuit.

9. The optical waveguide of claim 8, wherein the overlapping ranges
provide at least one overall temperature range in which at least partial
resonance occurs at any temperature within the overall temperature range.

10. The optical waveguide of claim 9, wherein the at least partial
resonance at any temperature within the overall temperature range results
in modulation of the first frequency at any temperature within the
overall temperature range.

11. The optical waveguide of claim 10, wherein the modulation depth of
the first frequency at any temperature within the overall temperature
range is constant.

12. The optical waveguide of claim 2, wherein each of the plurality of
modulator circuits is driven by a common signal.

13. The optical waveguide of claim 2, further comprising a temperature
sensor and a control circuit that uses the temperature sensed by the
temperature sensor to apply driving signals to the plurality of modulator
circuits.

14. A silicon optical waveguide, comprising: a silicon optical
transmission channel for transmitting an optical signal input to the
optical waveguide with a first frequency; and a plurality of modulator
circuits configured along the silicon optical transmission channel, each
modulator circuit comprising an input resonant switch coupled to the
silicon optical transmission channel, an output resonant switch coupled
to the silicon optical transmission channel, and a modulator coupled in
between the input and output resonant switches, at least the input
resonant switch configured to resonate at the first frequency when the
modulator circuit that includes the input resonant switch is at a
resonant temperature, each modulator circuit having a different resonant
temperature.

15. The silicon optical waveguide of claim 14, wherein the input switch
in each modulator circuit is resonant at temperatures within a range of
temperatures bounding the respective modulator circuit's resonant
temperature.

16. The silicon optical waveguide of claim 15, wherein the ranges of
temperatures that each correspond to one of the plurality of modulator
circuits overlap each other to provide an overall temperature range
wherein resonance at the first frequency occurs at any temperature within
the overall temperature range.

17. The silicon optical waveguide of claim 16, wherein the modulation
depth of the first frequency at any temperature within the overall
temperature range is constant.

18. The silicon optical waveguide of claim 16, wherein the modulation of
the first frequency at any temperature within the overall temperature
range is between a minimum and a maximum modulation depth, wherein the
minimum modulation depth is at least seventy percent of the maximum
modulation depth.

19. A silicon optical waveguide, comprising: a silicon optical
transmission channel for transmitting an optical signal input to the
optical waveguide with a first frequency; and a plurality of modulators
configured along the silicon optical transmission channel, each modulator
configured to resonate at the first frequency at a corresponding resonant
temperature, each modulator having a different resonant temperature.

20. The silicon optical waveguide of claim 19, wherein each modulator is
resonant at temperatures within a range of temperatures bounding the
modulator's resonant temperature.

21. The silicon optical waveguide of claim 20, wherein the ranges of
temperatures that each correspond to one of the plurality of modulators
overlap each other to provide an overall temperature range wherein
resonance at the first frequency occurs at any temperature within the
overall temperature range.

22. The silicon optical waveguide of claim 21, wherein the modulation
depth of the first frequency at any temperature within the overall
temperature range is constant.

23. The silicon optical waveguide of claim 19, further comprising a
temperature sensor and a control circuit that uses the temperature sensed
by the temperature sensor to apply driving signals to the plurality of
modulators.

24. A processor system, comprising: a processor that includes at least
one silicon optical waveguide, comprising: silicon optical transmission
channel for transmitting an optical signal input to the optical waveguide
with a first frequency; and a plurality of modulator circuits configured
along the silicon optical transmission channel, each modulator circuit
comprising at least one resonant structure that resonates at the first
frequency when the modulator circuit that includes the at least one
resonant structure is at a resonant temperature, each modulator circuit
having a different resonant temperature.

25. The processor system of claim 24, wherein the at least one resonant
structure is an optical modulator coupled to the silicon optical
transmission channel.

26. The processor system of claim 24, wherein the plurality of modulator
circuits each include an optical modulator coupled to the silicon optical
transmission channel via an input switch and an output switch.

27. The processor system of claim 26, wherein the at least one resonant
structure is the input switch.

28. The processor system of claim 24, wherein the at least one resonant
structure is resonant at temperatures within a range of temperatures
bounding the modulator circuit's resonant temperature.

29. The processor system of claim 28, wherein the ranges of temperatures
that each correspond to one of the plurality of modulator circuits
overlap each other to provide an overall temperature range wherein
resonance at the first frequency occurs at any temperature within the
overall temperature range.

30. The processor system of claim 29, wherein the modulation depth of the
first frequency at any temperature within the overall temperature range
is constant.

31. The processor system of claim 24, wherein each of the plurality of
modulator circuits is driven by a common signal.

32. The processor system of claim 24, further comprising a temperature
sensor and a control circuit that uses the temperature sensed by the
temperature sensor to apply driving signals to the plurality of modulator
circuits.

33. A method of using a silicon optical waveguide within a range of
temperatures, comprising: inputting an optical signal of a first
frequency to an optical transmission channel; modulating said optical
signal when a temperature of the silicon optical waveguide is equal to a
first temperature, said modulating performed using a first modulator
circuit that includes a first resonant structure with a corresponding
first resonant temperature, said first resonant temperature being equal
to said first temperature; and modulating said optical signal when a
temperature of the silicon optical waveguide is equal to a second
temperature, said modulating performed using a second modulator circuit
that includes a second resonant structure with a corresponding second
resonant temperature, said second resonant temperature being equal to
said second temperature.

34. The method of claim 33, further comprising: modulating said optical
signal when a temperature of the silicon optical waveguide is equal to a
third temperature, said third temperature being in between said first and
second temperatures, said modulating performed using said first and
second modulator circuits during partial resonance of said circuits'
corresponding first and second resonant structures.

35. The method of claim 34, further comprising filtering said optical
signal by using the first and second resonant structures.

36. The method of claim 35, wherein said filtering step uses first and
second resonant structures which are both ring resonator optical
switches.

37. The method of claim 35, wherein said filtering step uses first and
second resonant structures which are both ring resonant modulators.

38. The method of claim 34, further comprises modulating said optical
signal at said first frequency to a modulation depth that is constant at
first, second and third temperatures.

39. The method of claim 34, further comprising driving said first and
second modulator circuits using a common signal.

40. The method of claim 34, further comprising using a temperature sensor
and a control circuit that uses the temperature sensed by the temperature
sensor to apply driving signals to said first and second modulator
circuits.

Description:

FIELD OF THE INVENTION

[0001] The embodiments of the invention relate generally to the field of
silicon optical waveguides and, more particularly, to optical modulating
circuits in silicon optical waveguides.

BACKGROUND OF THE INVENTION

[0002] Silicon-based integrated circuits have long been used as a platform
for microelectronic applications. For example, microprocessors in
computers, automobiles, avionics, mobile devices, control and display
systems and in all manner of consumer and industrial electronics products
are all traditionally based on a silicon platform that facilitates and
directs the flow of electricity. As processing requirements have
increased, the design of silicon-based integrated circuits has adapted to
accommodate for faster processing times and increased communication
bandwidths. Primarily, such performance gains have been the result of
improvements in feature density, meaning that technologies have been
developed to crowd ever-increasing numbers of features such as
transistors onto a silicon chip. While efforts to increase feature
density continue, alternative methods for increasing processing speeds
and bandwidth on silicon-based platforms are also being developed. One
such method is known as silicon photonics.

[0003] The term "silicon photonics" relates to the study and application
of photonic systems that use silicon as an optical medium. Thus, instead
of or in addition to using silicon to facilitate the flow of electricity,
silicon is used to direct the flow of photons or light. While the speed
of electricity and the speed of light are the same, light is able to
carry data over a wider range of frequencies than electricity, meaning
that the bandwidth of light is greater than that of electricity. Thus, a
stream of light can carry more data than a comparable stream of
electricity can during the same period of time. Accordingly, there are
significant advantages to using light as a data carrier. Furthermore,
using silicon as a preferred optical medium allows for application of and
tight integration with existing silicon integrated circuit technologies.
Silicon is transparent to infrared light with wavelengths above about 1.1
micrometers. Silicon also has a high refractive index of about 3.5. The
tight optical confinement provided by this high index allows for
microscopic optical waveguides, which may have cross-sectional dimensions
of only a few hundred nanometers, thus facilitating integration with
current nanoscale semiconductor technologies. Thus, silicon photonic
devices can be made using existing semiconductor fabrication techniques,
and because silicon is already used as the substrate for most integrated
circuits, it is possible to create hybrid devices in which the optical
and electronic components are integrated onto a single microchip.

[0004] In practice, silicon photonics are implemented using
silicon-on-insulator, or SOI, technology. In order for the silicon
photonic components to remain optically independent from the bulk silicon
of the wafer on which they are fabricated, it is necessary to have an
intervening material. This is usually silica, which has a much lower
refractive index of about 1.44 in the wavelength region of interest. This
results in total internal reflection of light at the silicon-silica
interface and thus transmitted light remains in the silicon.

[0005] A typical example of data propagation using light is illustrated in
FIG. 1. FIG. 1 illustrates an optical transmission system 100 that
includes, for example, a silicon waveguide 110. The silicon waveguide may
make up the entirety of the optical transmission system 100 or just one
or more portions of the system 100. The system includes multiple data
input channels 120, where each channel 120 transmits data in the form of
pulses of light. In order to simultaneously transmit the data carried on
the multiple data channels 120, the light in each channel 120 is
modulated by a frequency modulator 130. The modulated light from each
channel 120 is then combined into a single transmission channel 150 using
an optical multiplexer 140. The multiplexed light is then transmitted
along the single transmission channel 150 to an endpoint (not shown)
where the light is de-multiplexed and demodulated before being used by an
endpoint device.

[0006] Transmission of light in an optical waveguide is, however, affected
by temperature. In general, changes in temperature can result in changes
in the device dimensions (due to thermal expansion) and refractive
indices of the materials used in the optical waveguide. More
particularly, changes in temperature can affect the operation of the
optical frequency modulators 130 illustrated in FIG. 1. Resonant photonic
modulators are designed to only modulate received frequencies that are at
or close to specific known frequencies. To only allow the modulation of
the specific known frequencies, the modulators include resonant
structures that act to filter out all but the known frequencies which are
to be modulated by the modulators. Thus, the known frequencies are
resonant frequencies of the resonant structures. Unfortunately, because
the refractive indices of the resonant structures tend to change
according to temperature, the specific frequencies that are modulated
(i.e., the resonant frequencies) tend to deviate from the known
frequencies as the temperature changes. Therefore, there is a need for
silicon optical waveguides with modulator circuits that are tolerant of
changes in temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 illustrates an optical transmission system with a silicon
optical waveguide.

[0008]FIG. 2 illustrates a silicon optical waveguide in accordance with a
disclosed embodiment.

[0009]FIG. 3 illustrates a frequency/intensity graph for a ring resonator
in accordance with a disclosed embodiment.

[0010]FIG. 4 illustrates a method of operating a silicon optical
waveguide in accordance with a disclosed embodiment.

[0011]FIG. 5 illustrates a frequency/intensity graph for a silicon
optical waveguide in accordance with a disclosed embodiment.

[0012]FIG. 6 illustrates a silicon optical waveguide in accordance with a
disclosed embodiment.

[0013] FIG. 7 illustrates a frequency/intensity graph for a silicon
optical waveguide in accordance with a disclosed embodiment.

[0014] FIG. 8 illustrates a method of operating a silicon optical
waveguide in accordance with a disclosed embodiment.

[0016]FIG. 10 illustrates a processor system in accordance with a
disclosed embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Because silicon-based integrated circuits are used in a variety of
products and circumstances, silicon-based integrated circuits are likely
to be exposed to a wide range of temperature conditions. In silicon-based
optical waveguides, however, temperature fluctuations can result in
decreased performance of included optical frequency modulators.
Therefore, in order to enable a silicon optical waveguide to be more
robust to temperature changes, an improved silicon optical waveguide with
optical frequency modulators is herein disclosed.

[0018] One embodiment of an improved silicon optical waveguide 210 is
illustrated in FIG. 2. The illustrated portion of the improved waveguide
210 includes an optical transmission channel 220 and two frequency
modulator circuits 230T1, 230T2, each serially coupled to the waveguide
210. While only two frequency modulator circuits (referred to generally
as 230) are illustrated, the improved silicon optical waveguide 210 could
include any number of frequency modulator circuits 230, as will become
clear in the following explanation. In FIG. 2, each modulator circuit 230
includes two switches (e.g., switches 240AT1, 240BT1) and a modulator
(e.g., modulator 250T1). The switches (referred to generally as 240) are
coupled to the waveguide 210 so as to allow optical signals of a specific
frequency to be shunted from the waveguide 210 to a modulator (referred
to generally as 250) which is configured in parallel with the waveguide
210. Thus, because the switches 240 are tuned to allow specific
frequencies of optical signals access to the modulators 250, the switches
240 act like band-pass filters that provide filtered signals to the
modulators 250. Optical signals that are not of the specific frequencies
are allowed to continue without obstruction along the waveguide 210.

[0019] In each modulator circuit 230, one switch (e.g., switch 240AT1) is
designated as an input switch (referred to generally as input switch
240A). The other switch in the modulator circuit 230, e.g., switch
240BT1, is designated as an output switch (referred to generally as
output switch 240B). The input switch 240A couples optical signals from
the optical transmission channel 220 to the modulator 250. The output
switch 240B couples optical signals from the modulator 250 back to the
optical transmission channel 220.

[0020] The switch frequency response is a result of the resonant
properties of the switch 240. Resonant optical switches are switches that
only fully pass or allow transmission of signals that have frequencies
that match the switch resonant frequency. For example, a ring resonator
switch is essentially a looped optical waveguide whose circumference
allows for constructive interference of a desired frequency. An optical
ring resonator whose circumference is equal to an integer-multiple of an
optical signal's wavelength (e.g., λ, 2λ, 3λ, etc.)
that corresponds to a desired frequency will fully pass or transmit a
signal with the desired frequency because the signal experiences
constructive interference as it travels around the optical ring
resonator. Conversely, the same optical ring resonator will fully block
an optical signal where the ring resonator's circumference is equal to an
odd-numbered integer-multiple of one-half of the optical signal's
wavelength (e.g., (1/2)λ, (3/2)λ, (5/2)λ, etc.) due to
the destructive interference that is generated. The optical ring
resonator will only partially pass other frequencies.

[0021] The frequency-pass characteristics of a ring resonator are
illustrated in the graph 300 of FIG. 3. For a given temperature T0, a
ring resonator will fully pass a signal at the ring's resonant frequency
ω0. This is evidenced in the graph 300 by the deep trough at
frequency ω0, which indicates the ring resonator is significantly
more sensitive to signals at frequency ω0 than at other
frequencies. Signals at frequencies that are far away from frequency
ω0 are essentially blocked while signals at frequencies near
frequency ω0 are only partially blocked. However, if the
temperature changes to temperature T1, then the resonant frequency of the
ring resonator is shifted to frequency ω1. Thus, the ring resonator
acts as a temperature-dependent band-pass filter for the ring's resonant
frequency.

[0022] Returning to FIG. 2, the ring resonator switches 24 provide
filtered access to the optical modulators 250. The optical modulators 250
may be resonant modulators or any other type of frequency modulator. Like
the switches 240, a resonant modulator is tuned to function at a specific
temperature. Thus, as an example, a resonant modulator in series with a
resonant switch is generally tuned to function at a temperature T0 that
corresponds with the temperature T0 at which the switch passes a resonant
frequency ω0. The optical modulators may also be of a non-resonant
type. Irregardless, the resonant modulators 250 are driven by a common
signal 260 to modulate the received frequency ω0 received via input
switch 240A. The common signal 260 functions to inject charge into the
modulators 250, thus altering the index of refraction of the modulators
250 in order to effectuate a frequency modulation. The modulated
frequency is then coupled back onto the optical transmission channel 220
via output switch 240B.

[0023] In FIG. 2, each modulator circuit is tuned to a specific
temperature. In other words, the switches 240 and modulator 250 within
each modulator circuit 230 are selected and/or designed to filter and
modulate a specific frequency at a specific temperature. In order to
compensate for changes in temperature, each modulator circuit 230 is
tuned to a temperature that is different from the tuned-temperature of
the other modulator circuits 230. Thus, when one modulator circuit is
inactive because the temperature is different from its tuned temperature,
another modulator circuit whose tuned temperature corresponds with the
actual temperature is active. In this way, the waveguide 210 is designed
to accommodate frequency modulation at a variety of temperatures.

[0024] A method 400 of operation of the waveguide 210 of FIG. 2 is
illustrated in FIG. 4. Initially, a laser input of a given frequency
ω0 is input to the waveguide (step 410). The input frequency
ω0 is to be modulated using one or more modulator circuits,
depending on the waveguide temperature T. The modulator circuits are each
tuned to modulate frequency ω0 at different temperatures. Thus, for
example, modulator circuit 230T1 is tuned to modulate frequency ω0
at temperature T1. Modulator circuit 230T2 is tuned to modulate frequency
ω0 at temperature T2 which differs from temperature T1. Additional
modulator circuits 230TN may be included that each modulate frequency
ω0 (step 430) at respective temperatures TN (step 420).

[0025] An intensity versus temperature graph 500 showing the response of
all of the modulator circuits 230 at frequency ω0 is illustrated in
FIG. 5. The graph illustrates that for a given frequency ω0, each
modulator circuit is active within a different temperature range. For
example, at temperature T1, modulator circuit 230T1 is fully active and
no other modulator circuit is active. At temperature T2, modulator
circuit 230T2 is fully active and no other modulator circuit is active.
Similarly, at temperature TN, modulator circuit 230TN is fully active. At
temperatures in between temperatures T1 and T2, both modulator circuits
230T1 and 23012 are only partially active.

[0026] Graph 500 also illustrates the modulation depth or degree of
modulation provided by the waveguide 210 at different temperatures T. For
example, at temperature T1, the illustrated modulation depth is
approximately -20 dB. At temperature T2, the illustrated modulation depth
is also approximately -20 dB. However, at a temperature in between
temperatures T1 and T2, the modulation depth provided by any one
modulator circuit 230 is substantially less than -20 dB. Nevertheless,
because of the overlap in modulator circuit activity, at temperatures in
between temperatures T1 and T2, both modulator circuits 230T1 and 230T2
provide some modulation. The total modulation depth provided is thus the
sum of overlapping modulation depths provided by individual modulator
circuits 230.

[0027] It is possible to design a modulator array with a variable
frequency response versus temperature graph so that overlapping of
modulation depths only involves a few devices at any given temperature.
Thus, during operation of the waveguide, if the waveguide temperature T
is equal to temperature T1, modulator circuit 230T1 is active in
modulating the received frequency ω0 while other modulator circuits
230T2, 230TN are not active. If the waveguide temperature T changes and
equals temperature T2, modulator circuit 230T2 becomes active in
modulating the received frequency ω0 while the other modulator
circuits 230T1, 230TN are not active. If the waveguide temperature T
changes and equals a temperature in between temperatures T1 and T2, both
modulator circuits 230T1 and 230T2 become partially active in modulating
the received frequency ω0 at a reduced modulation depth, though the
modulator circuits 230T1 and 230T2 may be designed and configured so that
the sum of modulation from both modulator circuits 230T1, 230T2 may be
approximately equal to the maximum modulation depth of any individual
modulator circuit 230. This is the result when the modulation ranges of
neighboring modulator circuits 230 overlap at a point where each
modulator circuit's modulation depth is approximately one-half of the
circuit's maximum modulation depth. Alternatively, some variance in
modulation depth may be tolerated. For example, depending on the
waveguide system's noise tolerance, a modulation depth of seventy-percent
of the maximum modulation depth may be tolerated.

[0028] Thus, the optical waveguide system facilitates frequency modulation
within a range of temperatures, where the temperature range is dependent
upon the number of modulator circuits placed in series in the waveguide
and the characteristics (e.g., the frequency/temperature response) of the
modulator circuits.

[0029] In another embodiment, the resonant switches are removed and only
resonant ring modulators are provided in series with the optical
waveguide. FIG. 6 illustrates this "switchless" embodiment of an optical
waveguide 610. In the embodiment of FIG. 6, two or more modulators
(referred to generally as modulators 650) are positioned in series along
the waveguide 610. The modulators 650 are selected and/or designed to be
resonant at a frequency ω0 at different temperatures. Or, in other
words, for a given temperature T, each modulator has a different resonant
frequency. The resonant frequencies of neighboring modulators 650 are
offset such that modulation overlap between the neighboring modulators
650 occurs with a modulation depth for each modulator 650 equal to
approximately one-half their greatest modulation depth, as illustrated in
FIG. 7. Thus, at a given temperature, T1, the optical circuit is designed
such that a first modulator 650T1 is resonant. At a temperature T2, the
first modulator 650T1 is no longer resonant, but a second modulator 650T2
is resonant. At a temperature T3 in between temperatures T1 and T2, both
the first and second modulators 650T1, 650T2 are partially resonant. In
this way, by cascading multiple modulators 650 in series with the optical
transmission channel 220, the optical waveguide 610 is made to be more
robust against fluctuations in temperature. The number of modulators 650
used in the waveguide 610 is not limited except by considerations of
cost, space and overall need.

[0030] A method 800 of operation of the waveguide system of FIG. 6 is
illustrated in FIG. 8. Initially, a laser input of a given frequency
ω0 is input to the waveguide (step 810). The input frequency
ω0 is to be modulated using one or more modulators, depending on
the waveguide temperature T. The modulators are each tuned to modulate
frequency ω0 at different temperatures. Thus, for example,
modulator 650T1 is tuned to modulate frequency ω0 at temperature
T1. Modulator 650T2 is tuned to modulate frequency ω0 at
temperature T2 which differs from temperature T1. Additional modulators
650TN may be included that each modulate frequency ω0 (step 830) at
respective temperatures TN (step 820).

[0031] During operation of the waveguide, if the waveguide temperature T
is equal to temperature T1, modulator 650T1 is active in modulating the
received frequency ω0 while other modulators 650T2, 650TN are not
active. If the waveguide temperature T changes and equals temperature T2,
modulator 650T2 becomes active in modulating the received frequency
ω0 while the other modulators 650T1, 650TN are not active. If the
waveguide temperature T changes and equals a temperature in between
temperatures T1 and T2, both modulators 650T1 and 650T2 become partially
active in modulating the received frequency ω0 at a reduced
modulation depth. Both modulators are driven from the same signal, and
hence both can work in conjunction to encode the signal on the received
frequency ω0.

[0032] The waveguides 210, 610 may additionally be modified as illustrated
in FIGS. 9A and 9B. In FIGS. 9A and 9B, waveguides 910A and 910B,
respectively, are modified by the addition of a temperature sensor 920
and a control circuit 960. In the waveguides 910A, 910B, operation of the
modulators 250, 650 is optimized by using a temperature sensor 920 whose
output enables a control circuit 960 to actively drive the modulators
250, 650. For example, a control algorithm could be used to use the
sensed temperature of the optical waveguide to drive specific modulators
at specific sensed temperatures. In this way, specific modulators may be
driven to provide greater modulation depth for given frequencies than the
modulation depth provided by a purely passive modulation circuit.
Additionally, the sensed temperature information may be used to help
generate specific wavelengths for transmission along the waveguide so
that the generated wavelengths correspond to those that the other side of
the communications link or waveguide expects to receive.

[0033] The improved optical waveguides may be fabricated as part of an
integrated circuit. The corresponding integrated circuits may be utilized
in a typical processor system. For example, FIG. 10 illustrates a typical
processor system 1500 which includes a processor and/or memory device
employing improved silicon optical waveguides such as optical waveguides
210, 610, 910A, 910B in accordance with the above described embodiments.
A processor system, such as a computer system, generally comprises a
central processing unit (CPU) 1510, such as a microprocessor, a digital
signal processor, or other programmable digital logic devices, which
communicates with an input/output (I/O) device 1520 over a bus 1590. A
memory device 1400 communicates with the CPU 1510 over bus 1590 typically
through a memory controller. The memory device may include RAM, a hard
drive, a FLASH drive or removable memory for example. In the case of a
computer system, the processor system may include peripheral devices such
as removable media devices 1550 which communicate with CPU 1510 over the
bus 1590. If desired, the memory device 1400 may be combined with the
processor, for example CPU 1510, as a single integrated circuit.

[0034] Any one or more of the components of the processor system 1500 may
include one or more of the silicon optical waveguides described above.
For example, CPU 1510, I/O device 1520 and memory device 1400 may include
silicon optical waveguides. In addition, communication between two or
more of the processor system components via bus 1590 may be via silicon
optical waveguides 210, 610, 910A, 910B.

[0035] The above description and drawings should only be considered
illustrative of exemplary embodiments that achieve the features and
advantages described herein. Modification and substitutions to specific
process conditions and structures can be made. Accordingly, the invention
is not to be considered as being limited by the foregoing description and
drawings, but is only limited by the scope of the appended claims.